Methyl 3-phenyl-2(E)-propenyl 1,4-dihydro2,6-dimethyl-4-(3-nitrophenyl)pyridine-3,5-dicarboxylate (hereinafter referred to as the "compound") has effective pharmacological activities for example antihypertensive effect and others, which have been developed by the present inventors [Japanese Patent Kokai (Laid-open) No. 60-120861 (1985), and European Patent Publication No. 0,145,434 (June 19, 1985)]. However, the compound is practically insoluble in an aqueous solution (0.5 .mu.g/ml), and has quite a low absorbability rate through the gastrointestinal tract when it is administered orally.
The present inventors have made an extensive study to improve the solubility of the compound in an aqueous solution, so as to make it possible to sustain a supersaturated state thereof for a long period of time, and to improve the absorbability thereof through the gastrointestinal tract. During the course of study, the present inventors tried to improve the solubility thereof in an aqueous solution by making it in an amorphous state with various types of polymers. However, using polymers such as a cellulose-type high molecular compound or a polyvinylpyrrolidone or the like, the solubility of the compound was not improved. Accordingly, the present inventors continued the study and finally found that the object of the present invention can be achieved only if the compound is made in the amorphous state using pH-dependent type copolymers of methacrylic acid and its derivatives.